Strong Plasmonic Enhancement of a Single Peridinin–Chlorophyll <i>a</i>–Protein Complex on DNA Origami-Based Optical Antennas

In this contribution, we fabricate hybrid constructs based on a natural light-harvesting complex, peridinin–chlorophyll <i>a</i>–protein, coupled to dimer optical antennas self-assembled with the help of the DNA origami technique. This approach enables controlled positioning of individual complexes at the hotspot of the optical antennas based on large, colloidal gold and silver nanoparticles. Our approach allows us to selectively excite the different pigments present in the harvesting complex, reaching a fluorescence enhancement of 500-fold. This work expands the range of self-assembled functional hybrid constructs for harvesting sunlight and can be further developed for other pigment–proteins and proteins

Broadband Fluorescence Enhancement with Self-Assembled Silver Nanoparticle Optical Antennas

Plasmonic structures are known to affect the fluorescence properties of dyes placed in close proximity. This effect has been exploited in combination with single-molecule techniques for several applications in the field of biosensing. Among these plasmonic structures, top-down zero-mode waveguides stand out due to their broadband capabilities. In contrast, optical antennas based on gold nanostructures exhibit fluorescence enhancement on a narrow fraction of the visible spectrum typically restricted to the red to near-infrared region. In this contribution, we exploit the DNA origami technique to self-assemble optical antennas based on large (80 nm) silver nanoparticles. We have studied the performance of these antennas with far- and near-field simulations and characterized them experimentally with single-molecule fluorescence measurements. We demonstrate that silver-based optical antennas can yield a fluorescence enhancement of more than 2 orders of magnitude throughout the visible spectral range for high intrinsic quantum yield dyes. Additionally, a comparison between the performance of gold and silver-based antennas is included. The results indicate that silver-based antennas strongly outperform their gold counterparts in the blue and green ranges and exhibit marginal differences in the red range. These characteristics render silver-based optical antennas ready for applications involving several fluorescently labeled species across the visible spectrum

Axial Colocalization of Single Molecules with Nanometer Accuracy Using Metal-Induced Energy Transfer

Single-molecule localization based super-resolution microscopy has revolutionized optical microscopy and routinely allows for resolving structural details down to a few nanometers. However, there exists a rather large discrepancy between lateral and axial localization accuracy, the latter typically three to five times worse than the former. Here, we use single-molecule metal-induced energy transfer (smMIET) to localize single molecules along the optical axis, and to measure their axial distance with an accuracy of 5 nm. smMIET relies only on fluorescence lifetime measurements and does not require additional complex optical setups

Nano–bio interactions of upconversion nanoparticles at subcellular level: biodistribution and cytotoxicity

Background: Modern medicine requires intensive research to find new diagnostic and therapeutic solutions. Recently, upconverting nanoparticles (UCNPs) doped with lanthanide ions have attracted significant attention. Methods: The efficient internalization of UCNPs by cells was confirmed, and their precise cellular localization was determined by electron microscopy and confocal studies. Results: UCNPs colocalized only with specific organelles, such as early endosomes, late endosomes and lysosomes. Furthermore, experiments with chemical inhibitors confirmed the involvement of endocytosis in UCNPs internalization and helped select several mechanisms involved in internalization. Exposure to selected UCNPs concentrations did not show significant cytotoxicity, induction of oxidative stress or ultrastructural changes in cells. Conclusion: This study suggests that UCNPs offer new diagnostic options for biomedical infrared imaging.</p